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You can look up the selected value using the control name, and you can use code such as this to reset the proper selected index: protected void Page_Load(object sender, EventArgs e) { for (int i = 0; i < 1000; i++) { lstBigItemsAdd(iToString()); } if (PageIsPostBack) { lstBigSelectedItemText = RequestForm["lstBig"]; } }.

OpenWebConfiguration() OpenMachineConfiguration()

ASP .NET includes a variety of options for state management. It features the same Session and Application state collections as traditional ASP (with a few enhancements) and an entirely new view state model. ASP.NET even includes a caching system that allows you to retain information without sacrificing server scalability. Each state management choice has a different lifetime, scope, performance overhead, and level of support. Table 6-1, Table 6-2, and Table 6-3 show an at-a-glance comparison of your state management options. Table 6-1. State Management Options Compared (Part 1)

Clearly, this could represent a situation where you need to rethink your user interface to be more usable. For example, a better design might be to ask the user a preliminary question to narrow down the number of list entries. You might even want to model the whole process with a Wizard control. But assuming you really do need a list with a huge number of entries, you ll need to understand how to optimize its view state usage.

RefreshSection()

Allowed Data Types Storage Location All serializable .NET data types. A hidden field in the current web page.

As described in earlier chapters, view state information is stored in a single Base64-encoded string that looks like this: <input type="hidden" name="__VIEWSTATE" value="dDw3NDg2NTI5MDg7Oz4="/> Because this value isn t formatted as clear text, many ASP.NET programmers assume that their view state data is encrypted. It isn t. A clever hacker could reverse-engineer this string and examine your view state data in a matter of seconds, as demonstrated in 3. If you want to make view state secure, you have two choices. First, you can make sure that the view state information is tamper-proof by using a hash code. You do this by adding the EnableViewStateMAC attribute to the Page directive in your .aspx file, as shown here: <%@ Page EnableViewStateMAC="true" %> A hash code is a cryptographically strong checksum. Essentially, ASP.NET calculates this checksum based on the current view state content and adds it to the hidden input field when it returns the page. When the page is posted back, ASP.NET recalculates the checksum and ensures that it matches. If a malicious user changes the view state data, ASP.NET will be able to detect the change, and it will reject the postback. Hash codes are enabled by default, so if you want this functionality, you don t need to take any extra steps. Occasionally, developers choose to disable this feature to prevent problems in a web farm where different servers have different keys. (The problem occurs if the page is posted back and handled by a new server, which won t be able to verify the view state information.) To disable hash codes, you can use the enableViewStateMac attribute of the <pages> element in the web.config or machine.config file, as shown here: <configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0"> <system.web> <pages enableViewStateMac="false" /> ... </system.web> </configuration>

You need to consider a number of factors when using these methods. When you retrieve information using the WebConfigurationManager.OpenWebConfiguration() method, it reflects the cumulative configuration for the current application. That means settings from the current web.config file are merged with those defined higher up the configuration hierarchy (for example, in a parent directory or in the machine.config file). To test this, you simply need to loop over the connection strings using code like this: foreach (ConnectionStringSettings connection in WebConfigurationManager.ConnectionStrings) { Response.Write("Name: " + connection.Name + "<br />"); Response.Write("Connection String: " + connection.ConnectionString + "<br /><br />"); }

String data. The client s computer (in memory or a small text file, depending on its lifetime settings). Set by the programmer. It can be used in multiple pages and can persist between visits. The whole ASP.NET application.